UNITED STATES DEPARTMENT OF THE INTERIOR J. A. KRUG, Secretary GEOLOGICAL SURVEY W. E. WRATHER, Director \ CIRCULAR 16 LATE PALEOZOIC ROCKS EXPOSED IN THE DUCHESNE RIVER AREA, DUCHESNE COUNTY, UTAH By John W. Huddle and Franklin T. McCann WASHINGTON 1947 UNITED STATES DEPARTMENT OF THE INTERIOR J. A. KRUG, Secretary GEOLOGICAL SURVEY W. E. WRATHER, Director CIRCULAR 16 LATE PALEOZOIC ROCKS EXPOSED IN THE DUCHESNE RIVER. AREA, DUCHESNE ·COUNTY, UTAH By John W. Huddle and Franklin T. McCann WASHINGTON 1947 . IATE PALEOZOIC ROCKS EXPOSED IN THE DUCHESNE RIVER AREA, DUCHESNE CO:tJNTY, UTAH. By John W. Huddle and Franklin T. McCann During 1945 two field parties of the U. S. Geological Survey investigated the stratigraphy and structure of the pre~Tertiary rocks on the south slope of the Uinta Mountains in northeastern Utah. The work was undertaken because of the increasing interest in the oil and gas possibilities of the Uinta Basin, which lies south of the Uinta Mountains. Geologic reports on these areas are in preparation but it seems advisable to present at this time a detailed section of the lata Paleozoic rocks in the Duchesne River area. The late Paleozoic rocks in the Duchesne River were/ first mappPd and described by Berkey (1905, pp. 517-530), and his work was followed by the reports of Emmons (1907, pp. 287-302), and Weeks (190')7, pp. 427-448), who recognized the same general sequence of rocks as Berkey described but disagreed regarding the thicknesses and correlations given by him. Detailed sections of the Permian and Carb~niferous formations in the Duchesne River area are inciuded in two recen~ articles by J. Stewart Williams (193~, P• 98; 1943, pp. 602-605). Late Paleozoic rocks are exposed in the canyon walls of Duchesne River and in tributary ca~ons, but only parts of the sequence are exposed at each place, and the section herein des.­ cribed is a composite of several outcrops. Because of the presence of numerous small faults a few of the thicknesses·could not be accurately determined. The inadequate exposures of ;r:art of the sequence of rocks and the presence of the small faults probably explain most or all the differences in thickness of certain units between our section and sections previously published·by others. On the south flank of the Uinta Mountains the beds of late Paleozoic limestone rest with angular unconformity on beds of quartzite and shale correlated with the Pine Valley quartzite or, where this formation is absent, on the Ophir (?) shale of Cambrian age (Forrester, 1937, p. 638). The Madison limestone of Mississippian age is about 245 'feet thick and consists mainly of thin-bedded, dark-gray fossiliferous'limestone; the lower part of the formation, 36 feet thick, consists of massive beds of dolomitic and sandy limestone. Typical ~adison limestone faunules were identified by James Steele Williams from beds that crop out along the North Fork of Duchesne River. A limestone formation about 600-650 feet thick; immediately overlying tne Madison limestone, is herein tentatively correlated with the Deseret limestone of the 2 1- • UTAH To Duchesne SK'ETCH MAP I OF THE O,UCHESNE RIVER AREA, UTAH SHOWING THE LOCATION:'' OF MEASURED SECTIONS 2 ;3 4 5 Formation Member Section Feet Character of rocks Woodside Reddish- brown s iUs tone shale Upper 00 150 Sandy dolomitic " Park City MiddiA 40 Block ohosohotic shale formation B r e c c i a, sa n d stone, and Lower :·:)"'\·:·:::·:· =:l, limestone .-.~ ~·::·:·.:.:. ::::~ ::: ~- (/) IJ.I a: C/)IJ.I (/) M.ossive, friable, very 950? fine grained sandstone to and sandy dolomitic 1,600 limestone 205 Reddish-brown sandstone and siltst.one Gray cherty I i me stone, 242 Lower -------- sandstone, and shale z 1 ·~ I t:. I ~ . Block shale and thin w Block shale 00-250 0 limestone beds a:: ·::::"*:~·:i:{~: m IJ.I Humbug ;;;;;: :::'\~}~ Breccia, sandstone, and 3 6 0 U>~~f=o~r~m~a~t~io~n~----~-J~~Y~t~~tf~t@~~WlJH]::': :!:::f/:::?::J:: __ _ _ __~·-I-im_e_s~t-on_e----~----------__j a: z / / ~ ~ 1~ I <t I /t> I Brown to gray, medium to a.. Deseret "'" I> 1 I> 1 o ~ li m e s to n e 1/ ~ I ~ I I I 16oo- s 50 thick-bedded 'limestone and do1omitlc limestone (f) I I I 1 J (/)(f)~------------------~~~._1~1~+-----~~------------------------~ Modi son Thin'l'bedded, gray, dense 245 :E limestone II me stone t-::~=------t-P-.-.n-e_V_a_l_le-y-----h..~08/;Bq Massive sandstone and 375+ ~85· quartzite ·-~·:+·:·:~:::~:: ·:··.~·:··.'·?: ~:~.:: ::~-:-:: ·.~ ·. ·:~. cong I om e rate :~·:.(): ··o:: :o: :.c,;: :c,: . :o: ·.. ~ .. :o~ · :·~ . .'·~ .. ·o· LATE PALEOZOIC ROCKS EXPOSED IN DUCHESNE RIVER AREA, UTAH wasatch (Baker, oral conun~ication) and Cquirrh Mountains (Gilluly, 1932J pp. 25-26)~ These beds in the Duchesne River area were included in the ~::ad:tson limestone in ear}.ier reports. The . forna tion is d isting,.liBhr:Jd f:::- o·:n the Jv1adis on :im.eston·e by its thicker bedding_, brown co:Lo:':, gre9-ter au~nbe:r of beds of dolomitic limestones, and by the cha:cact-e-r of its coral fauna. The con­ tact between the Madison and Deeeret limestone: however, is not everywhere easily dist:5.nguir-;hatle. · Fossils collected f:com the Deseret limestone were examined by James Steele Williams, who reported (personal communication) that though not definitely diagnostic, they probably are of post-!~disori age, as is the Deseret. A sequence of limestone and sandstone breccia about 360 feet thick overlies the Deseret limestone. Though no fossils were found in this formation, it is considered to be equivalent to the Humbug formation of the 1~satch and Oquirrh Mountains on the basis of similar litho logic character and s'tra t1g:ra phic position" The Hu:nbug forrr.ation of the Oquirrh Hountains was cor-related by Gillu:t_y ( 1932, pp. 26..-29) with part of the Brazer limento!:-Je of sm,_thea~tern Idaho. Overlying t::1e H•.1.'nbug forma.tion is a b }ac; k shale ~::..tll t a. !Jout 200-250 feet; :,td.ck, -that, :may be equivalent to par\j o:f the Manning C~nyor1 rJh.:tle of -~he ~Vasatch (Baker~ ora_:_ cor:rwn.mication) and Cquirrh }tcurlta:_!!S C..rilluly, 1932, pp .. 31-~34). The foTma·tiiun is _f;B.rtly exposed :in mudflows and landslides a::_e;ng 0uches~e River Canyon and .:.s ()et·Ler exposed in Soapstone Bas·tn and on the headwatc:~c o£' Blind Stream. Fos·sils collected from the black shale and e lso fr·om a limestone bed near the top of the fonr.ation a:re ccnsj_dered by James Steele Williams (personal ccnununication) and Helen Duncan as of post­ ~fadison Mississippian age, equivalent to part of the Brazer limestone" The rocks in an interval, about 450 feet thick, irr~ediately above the black shale .J are assigned to the Morgan forrration of the Penns;y<lvanj_an serj_es and are divided in to a lowe:c limestone · member and an uppel· El.S.nds cone member~ Tl1e lower mernbe:::-, which is abcn:o.L ~..'.u feat chick~ :t.C! COIH!)OSed chiefTy oi' limestone, The mega.fo.::si~:c cc·: lected from th'2 lower· member wh1le not c..;..agn.GtJtic_ are eonsJ.dered m.~obabJ~r of ea;··;v Penns~.--lvan]i=l.n age by James Steele W:i.~::_-_,dm:-; .. (p·arRott3.l c:,mmutJJ.cat.io;). Thom~~.son (19~5, p. 24) also regards them as early Pennsylvanian in age. Tbe upper member o£ the !v!o;:·gan fo:':'matl~X1 :..s al;~1.1t ?.05 feet thick and consist.<? chiefly of sand~r~one .. It is dia t.:i.tti?:UJ~bed bv its r•ed-brown colo:c. and the c·.;Ptac.;~;j lVith the 8VerJ.ylug Waber-" sandstone is grada ti.onal. No fossils we·ce found in the upper member of the ~~fo:cgan forma- tion, bui:. it is considered early Pennsylvanian in age. The Weber sandstone was not satisfactorily measured in the Duchesne River area because the uppermoct and iowermost, parts of 5 the formation are poorly exposed and the beds are cut by many small faults ..The thickness of the formation is probably about 1,500 to 1,600 feet in Rhoades Canyon, which is about 4 miles northwest of Stockmore Ranger Station;· about 950 feet immediately west of Stockmore Ranger Station; and abou~ 1,200 feet in the west wall of Duchesne Ri·ver canyon about l;i miles north of Stock­ more Ranger Station. The differences in the' thickness measured at these pla.ces may be real or they may be due to faulting. The formation consists largely of very fine grained sandstone, but includes a few beds of limestone interbedded with the sandstone throughout the formation. , Three members of the Park City formation were recognized in the Duchesne River area; they are a lower member of sandstone and limestone breccia, a middle member of black phosphatic shale, and an upper member of dolomitic limestone. all three members are here indicated, for convenience, as Permian, although the lower part of the typical Fark City formation is roferred to the Pennsylvanian. The lower member is about 270 feet thick and con­ sists largely of sandstone and limestone breccia, but includes some limestone beds. A few poorly preserved fossils that were collected from the lower member in sec. 11, r. 1 N., R. 9 W., about a mile northwest of Johnson's Mill, were considered not certainly diagnostic.by James Steele Williams (personal communi­ cation), but were thought to resemble the local Permian facies more than anv of the local Pennsvlvanian facies.